MEPC 39/6/1

ANNEX

Page 58

7.9 Test interval

The efficiency of the converter shall bc tested prior to each calibration of the NO3 analyser.

7.10 Efficiency requirement

The efficiency of thc converter shall not be less than 90%, but a higher efficiency of 95% is strongly recommended.

Note: If, with the analyser in the most commons range. the NO, converter cannot give a reduction from 80% to 20% according to 7.2 above, then the highest range whiieh will give the reduction shall be used.

Figure 1. Schematic of NO2 converter efficiency device

8 Interference effects with CO, CO2, NO, and O2 analysers

Gases present in the exhaust other than the one being analysed may interfere with the reading in several ways. Positive interference may occur in NI)IR and PMI) instruments where the interfering gas gives the same effect as the gas being measured, but to a lesser degree. Negative interference may occur in NDIR instruments by the interfering gas broadening the absorption band of the measured gas. and in CLD instruments by the interfering gas quenching the radiation. The interference cheeks in 8.1 and 8.2 below shall be performed prior to an annalyser's initial use and after major service intervals.

8.1 CO analyser interference check

Water and CO2 may interfere with the CO analyser performance. Therefore, a CO2 span gas having a concentration oaf 811 tin 11)01/of full scale of the maximum operating range used during testing shall be bubbled through water at room temperature and the analyser response recorded. The analyser shall not

MEPC 3916/I

ANNEX

Page 59

be more than 1% of full scale for ranges greater than or equal to 300 ppm or more than 3 ppm for rangesbelow 300 ppm.

8.2 NOx analyser quench checks

The two gases of concern for CLD (and HCLD) analysers are CO, and water vapour. Quench responses to these gases are proportional to their concentrations, and therefore require test techniques to determine the quench at the highest expected concentrations experienced during testing.

8.2.1 CO2 quench cheek

8.2.1.1 A C02 span gas having a concentration of 80 to 100% of full scale of the maximum operating range shall be passed through the NDIR analyser and the CO2 value recorded an A. It shall then be diluted approximately 50% with NO) span gas and passed through the NDIR and (H)CLD. with the CO2 and NO values recorded as B and C, respectively. The CO2 shall then be shut off and only the NO span gas shall be passed through the (H)CL.D and the NO) value recorded as D.

8.2.1.2 The quench shall be calculated as follows:

and shall not be greater than 3% of full scale.

where:

A = Undiluted CO2 concentration measured with NDIR %

B = Diluted CO2, concentration measured with NL)IR

C = Diluted NO concentration measured with (H)CLD ppm

D = Undiluted NO concentration measured with (H)CLD ppm

8.2.1.3 Alternative methods of diluting and quantifying of CO2 and NO span gas values, such as dynamic mixing/blending. may be used.

8.2.2 Water quench check

8.2.2.1 This cheek applies too wet gas concentration measurements only. The calculation of water quench shall take into consider dilution of the NO span gas with water vapour and sealing of water vapour concentration of the mixture to that expected during testing.

8.2.2.2 A NO span gas having a concentration of 80 to 100% of full scale of the normal operating range shall be passed through the (H)CLD and the NO value recorded at D. The NO span gas shall then be bubbled through water at room temperature and passed through the (H)CLD and the NO value recorded as C. The analyser's absolute operating pressure and the water temperature shall be determined and recorded as E and P. respectively. The mixture's saturation vapour pressure that corresponds to the bubbler water temperature (F) shall be determined and recorded as G. The water vapour concentration(in %) of the mixture shall be calculated as follows:

and recorded as PP. The expected diluted NO span gas (in water vapour) concentration shall be calculated as follows:

前ページ　　　目次へ　　　次ページ